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How Registrations Work
======================
With the Remote Procedure Call (RPC) messaging pattern in WAMP, any WAMP
client can register a procedure for remote calling (become a callee).
The procedure is registered for being called using a call URI (e.g.
"com.myapp.myprocedure1").
Note: There are some :doc:`specific rules regarding URI formatting ` .
The registration is with the WAMP router, and calls for the procedure
are also made to the router. The router then forwards a call to a
respective callee. Unlike with traditional RPCs, this means that the
caller does not have any knowledge of the callee's identity, and that
all calls are routed via a single connection between the caller and the
WAMP router respectively the callee and the WAMP router.
The callee receives a registration ID for the procedure it registers.
While the caller uses the procedure URI to call a procedure, calls to
the procedure from the WAMP router are made using this registration ID.
Using the registration ID, a callee can unregister the procedure at any
time.
As a default, exact matching is used for RPCs, i.e. a call is only
accepted (and routed to a callee) if a callee has registered for the
exact URI used by a caller. Additionally, pattern-based registrations are
possible, e.g. a callee could register a URI which is prefix-matched, so
that a registration for "com.myapp.create" would lead to calls for both
"com.myapp.create.user" and "com.myapp.create.device" to be accepted and
invoked on the callee. For more on this see
- :doc:`Pattern-Based Registrations ` .
As a default, a procedure can only be registered by a single callee. All
further registration attempts return an error. The routed nature of RPCs
as implemented by WAMP allows other patterns as well, i.e. multiple
registrations may be allowed, and the procedure is then invoked on the
last callee to register which is currently still connected. For more on
this see
- :doc:`Shared Registrations ` .
Clients can be notfied of events regarding the lifecycle of
registrations, and query for information about existing registrations
using the
- :doc:`Registration Meta-Events and Procedures `
A registered procedure can return a single result (the default) or a set
of results over time, see
- :doc:`Progressive Call Results `